Micro unmanned aerial vehicle and method of control therefor

ABSTRACT

A micro unmanned aerial vehicle or drone (“UAV”)  10  is remotely controlled through an HMI, although this remote control is supplemented by and selectively suppressed by an on-board controller. The controller operates to control the generation of a sonar bubble that generally encapsulates the UAV. The sonar bubble, which may be ultrasonic in nature, is produced by a multiplicity of sonar lobes generated by specific sonar emitters associated with each axis of movement for the UAV. The emitters produce individual and beamformed sonar lobes that partially overlap to provide stereo or bioptic data in the form of individual echo responses detected by axis-specific sonar detectors. In this way, the on-board controller is able to interpret and then generate 3-D spatial imaging of the physical environment in which the UAV is currently moving or positioned. The controller is therefore able to plot relative and absolute movement of the UAV through the 3-D space by recording measurements from on-board gyroscopes, magnetometers and accelerometers. Data from the sonar bubble can therefore both proactively prevent collisions with objects by imposing a corrective instruction to rotors and other flight control system and can also assess and compensate for sensor drift.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and the benefit of, PCT ApplicationSerial No. PCT/GB2013/052745, filed on Oct. 22, 2013, and entitled“MICRO UNMANNED AERIAL VEHICLE AND METHOD OF CONROL THEREFOR”, whichalso claims priority to and the benefit of Great Britain PatentApplication No. 1218963.5, entitled “MICRO UNMANNED AERIAL VEHICLE ANDMETHOD OF CONROL THEREFOR”, filed on Oct. 22, 2012. All of theaforementioned applications are incorporated by reference herein intheir entirety.

BACKGROUND TO THE INVENTION

The present invention relates, in general, to a unmanned aerial vehicle(UAV) and is particularly, but not exclusively, applicable to a flightcontrol system for a micro or nano UAV that is tasked withreconnaissance and covert data gathering for risk assessment. Moreparticularly, the present invention relates to control of a UAV using alocally generated sonar bubble.

SUMMARY OF THE PRIOR ART

In the design of military or surveillance UAV systems, it is necessaryfor the flight-control system to be responsive, robust and lightweight.Particularly, the agile manoeuvring of a UAV relies upon accurateoperational regulation of its individual motors that collectivelycontrol 3-dimensional movement of the UAV device in space and real time.Indeed, fine manoeuvring control is required to permit secure and safereconnoitre into buildings, with current line-of-sight systems entirelyfailing to mitigate anything that is not seen by the remote handler orwhich is only seen at a point that is too late to calculate a new flightpath given current flight control settings, such as speed or altitude.In fact, even a camera-based UAV system, transmission path delay ormulti-path interference experienced in radio frequency (RF) operationmay present sufficient delay to jeopardize or compromise the remote UAVdrone. Indeed, current line-of-sight systems require direct activecontrol.

Micro UAV technology is particularly interesting from the perspective ofinspection and reconnaissance since the small size unit can bemanoeuvred, under remote control, into small or dangerous areas todetermine and relay images of a threat or risk. The drone footprint fora micro UAV is usually in the region of a metre in size and oftensignificantly smaller, with a weight in the range of less than a fewhundred grams. This small size places considerable constraints onpayload and motor size, with the motor technology relying on batterycells (such as lithium ion technology) for power.

It has been known to make use of inertial navigation or inertialguidance systems in UAV technologies, but principally only in largerscale devices rather than micro UAV implementations. These inertialsystems support navigation/guidance through the use of a computer,motion sensors (i.e. accelerometers that measure linear acceleration)and rotation sensors (i.e. gyroscopes that determine pitch, roll and yawto support calculation of angular velocity) and magnetometers thatoperate continuously to determine and the to calculate, via deadreckoning approach, the position, orientation and vector (i.e. speed andmovement direction) of a moving object in the reference frame. Moreparticularly, by tracking both the current angular velocity of thesystem and the current linear acceleration of the system measuredrelative to the moving system, it is possible to determine the linearacceleration of the system in the inertial reference frame. As will beunderstood, performing a suitable integration on the inertialaccelerations yields the inertial velocities and inertia position of thesystem.

Once established against an initial reference condition at a referencepoint, an inertial navigation therefore does not reference externalsources and is immune to jamming. Inertia navigation systems are,however, relatively expensive and are nevertheless susceptible to drifterror. With the passage of time, small errors in the measurement ofacceleration and angular velocity are integrated into progressivelylarger errors in velocity, which are compounded into still greatererrors in position. Since the new position is calculated from theprevious calculated position and the measured acceleration and angularvelocity, these errors accumulate roughly proportionally to the timesince the initial position was input. In fact, drift can attributed totwo processes: i) an offset from zero arising when there's no movement;and ii) a sensor resolution that is insufficient to detect smallmovements, these errors accumulate over time and result in an error inthe calculated position. Moreover, in the context of drift in sensorsassociated with maintaining level flight or controlling roll or yawrates, continuous and unchecked drift can potentially criticallycompromise flight stability to the extent that the drone eventuallycrashes.

As such, the drift in inertial navigation is a real problem, althoughincreasingly more sophisticated and larger multi-axis sensors with veryhigh resolution can reduce (but not eliminate) the percentage drifterror.

It is therefore necessary for the position in an inertia navigationsystem to be periodically corrected by input from some other type ofnavigation system, such as GPS. However, GPS isn't necessarily alwaysavailable and, in any event, is likely to provide only an approximatelocation in the confines of a room in a building where there's noline-of-sight and/or where signal attenuating effects can compromiseaccurate position determination.

Clearly, large scale corrective systems do not fit well with therestriction imposed on weight, available power and the covert nature ofmicro or nano UAV drones.

Laser-based distance measuring systems, while extremely accurate,provide only a highly-directional beam. In any event, laser-basedsystems are relatively heavy and therefore generally incompatible withthe load constraints and energy resources associated with micro and nanoUAV drones.

CN201727964U describes a toy helicopter with a collision preventionsystem realised by six ultrasonic sensors installed on the top, at thebottom, in the front, in the rear and on the left and right sides of thetoy.

WO 2006/138387 relates to a system and method to detect an impendingcontact or collision between a subject vehicle, which may be anaircraft, a watercraft or a load-handling vehicle, and stationaryobjects or other vehicles in the vicinity of the subject vehicle. Thesystem comprises distance or motion-detecting sensors mounted atpositions on the subject vehicle at risk of such collision or contact,and alerting means, responsive to said sensors, to notify the operatorof the subject vehicle and/or the operators of such other vehicles inthe vicinity of the subject vehicle of the risk of a collision.Preferred embodiments comprise alerting means which indicate to theoperator of the subject vehicle which, if any, sensors detect an objectcloser to the subject vehicle than a predetermined distance of safeapproach.

U.S. Pat. No. 6,804,607 describes a collision avoidance system for anaircraft or other vehicle that monitors a sphere or other safetyzone/cocoon about the vehicle. A light-detecting camera or other sensorreceives a signal return if any object enters the safety cocoon. Once anobject is detected in the cocoon, a signal is sent to the onboard senseand avoid computer and corrective action is taken. The system is capableof autonomous operation, and is self-contained and does not requireadditional hardware installations on target vehicles. The size and shapeof the safety cocoon monitored by the sensors adjusts according to thespeed and motion vectors of the aircraft or other vehicle, so as tomaximize efficient use of sensor capabilities and minimize the size,cost and power requirements of the system.

WO 2010/137596 describes is a mobile body control device for detectingan object or the like present around the mobile body and detecting thedistance to the object and the outline of the object in order that themobile body can avoid an obstacle and can land on a flat locationwithout using any GPS device. The mobile body control device is mountedto a mobile body and used. The mobile body control device comprises anultrasonic sensor unit for measuring the distance to a peripheral objectin the vicinity thereof using an ultrasonic wave having a weakdirectivity and outputting vicinity information which is the result ofthe measurement and an infrared sensor unit for repetitivelytransmitting infrared radiation from the infrared sensor by vibrationinto a prescribed scope viewed from the mobile body, determining theoutline of an object within the prescribed scope, measuring the distanceto the outline, and outputting outline information which is the resultof the measurement.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided aUAV containing a drive system for propelling the UAV through a spatialenvironment: a controller for controlling the drive system andoverseeing operation of the UAV; a multiplicity of sonar emittersassociated with different axes of travel of the UAV, each sonar emitterproducing a sonar lobe extending outwardly in a specified directionalong each of said different axes of travel, the sonar lobes combiningto encapsulate the UAV in a sonar bubble; and a multiplicity of sonardetectors, each axis of travel associated with a plurality of sonardetectors, wherein the sonar detectors are coupled to the controller topermit the controller, in response to echoes reflected off objectswithin the sonar bubble, to interpret and then generate a 3 D image ofthe spatial environment in which the UAV is stationary or moving andwithin which spatial environment the objects are stationary or moving;and wherein the controller is configured or arranged automatically tomoderate the drive system in response to an assessed position of objectsin the 3-D image relative to the UAV such that the controllerindependently controls movement of the UAV through the spatialenvironment along each axes of travel.

In a preferred embodiment the sonar bubble is assembled from partiallyoverlapping three-dimensional spatial sonar lobes generated byrelatively inclined pairs of sonar emitters.

Preferably, at least two sonar detectors are associated with eachdirection long each axis of travel, and wherein the controller isconfigured or arranged to resolve detected variations at least one ofsignal strength and round trip timing for pings to and echoes fromobjects in the sonar bubble to assess a relative position and nature ofthose objects with respect to the UAV.

The UAV may further comprise: motion and position sensors configured tomeasure absolute movements of the UAV in 3-D space; and a memory forstoring the absolute movement of the UAV in the spatial environment asresolved by the controller having regard to the measure of absolutemovements and the 3-D image constructed from object data acquired fromuse of the sonar bubble.

Object data acquired from use of the sonar bubble can be used tocompensate for drift in at least one of the motion and position sensors.

In a second aspect of the invention there is provided a method ofcontrolling movement of a UAV through 3-D space, the method comprising:generating a sonar bubble that substantially encapsulates the UAV, thesonar bubble assembled from overlapping beamformed sonar lobes producedfrom sonar pings emanating from a multiplicity of sonar emitters on theUAV, the sonar emitters associated with directions of movement of theUAV through the 3-D space; in response to echoes reflected off objectswithin the sonar bubble following production of said beamformed sonarlobes and as detected by a multiplicity of sonar detectors on the UAV,having a controller in the UAV interpret and then generate a 3-D imageof the spatial environment in which the UAV is stationary or moving andwithin which spatial environment the objects are classified asstationary or moving; and having the controller independently andautomatically control movement of the UAV through the spatialenvironment by applying direct control to a drive system tasked witheffecting movement in each axis of travel.

Preferably, the method of further comprises: measuring absolutemovements of the UAV in 3-D space using motion and position sensors;storing in memory the absolute movement of the UAV in the spatialenvironment as resolved by the controller having regard to the measureof absolute movements and the 3-D image constructed from object dataacquired from use of the sonar bubble; and under automatic instructionfrom the controller and with reference to the memory, automaticallyre-tracing the movement of the UAV upon loss of an external controlsignal or upon receipt of an instruction received over a wireless link.

In some embodiments the method can include: establishing a hover mode inthe UAV; and based on distance measurement data to objects acquired fromuse of the sonar bubble, compensating for drift in at least one motionor position sensor in the UAV.

Accordingly, in a preferred embodiment, a micro unmanned aerial vehicleor drone is remotely controlled through an HMI, although this remotecontrol is supplemented by and selectively suppressed by an on-boardcontroller. The controller operates to control the generation of a sonarbubble that generally encapsulates the UAV. The sonar bubble, which maybe ultrasonic in nature, is produced by a multiplicity of sonar lobesgenerated by specific sonar emitters associated with each axis ofmovement for the UAV. The emitters produce individual and beamformedsonar lobes that partially overlap to provide stereo or bioptic data inthe form of individual echo responses detected by axis-specific sonardetectors. In this way, the on-board controller is able to interpret andthen generate 3-D spatial imaging of the physical environment in whichthe UAV is currently moving or positioned. The controller is thereforeable to plot relative and absolute movement of the UAV through the 3-Dspace by recording measurements from on-board gyroscopes, magnetometersand accelerometers. Data from the sonar bubble can therefore bothproactively prevent collisions with objects by imposing a correctiveinstruction to rotors and other flight control system and can alsoassess and compensate for sensor drift.

Advantageously, the present invention provides a UAV system having ahigh degree of self-awareness that supports a highly stableflight-control system capable of providing an effective collisionavoidance system. The UAV is therefore ideal for covert intelligencegathering and stealthy incursion, with the system controlled from aremote and thus generally safe location. In fact, the system of thepresent invention is sufficiently advanced so that it compensate fortemporary loss of direct RF control, since the system can be set up tobe self-regulating and is self-aware of its local environment. Thepreferred embodiment provides for a drone-based system that can plot themovement of the drone in 3-dimentional (3D) space and record allrelative movements to fractions of a degree and millimetre precision.

Beneficially, the present invention provides environmental awareness fora UAV system that can be used autonomously to counter drift andfurthermore provide enhanced (remote) control which benefits from alocal, on-board decision-making system that functions to avoidcollisions and/or UAV instability.

Furthermore, in being able to store a record (during ingress, forexample, into a building and reflecting sonar-recovered data andmonitored changes in gyroscopic, course heading and accelerometermeasurements) of relative movement of the UAV, reversal of record ofthose recorded movements permits the UAV's controller to execute a rapidand controlled automatic egress of the UAV from the building.

Beneficially, inertial guidance is furthermore improved by use of thesonar bubble in the UAV of the preferred embodiment. Particularly, in ahover state, detected changes in echo path bouncing off an object andrecovered at one or more sonar detectors implies a level of drift thatcan be identified, locked out and compensated by an internal controllerof the UAV; this means that on-board sensors in the UAV can be locallycalibrated by the local controller procedure. If the level of movementdetected by a sensor is greater than self-determined levels of driftassociated with that sensor, then the UAV's controller can resolve thatthe object is moveable and thus not part of the fixed environment. Inbuilding an accurate and current environmental map based on recordedsonar echos, the controller is therefore able to exclude obstacles thatmove with time.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will now be describedwith reference to the accompanying drawings, in which:

FIG. 1 is a plan view and schematic representation of a micro UAVaccording to a preferred embodiment of the present invention;

FIG. 2 is a side view of the micro UAV of FIG. 1;

FIG. 3 is shows a surface of the micro UAV of FIG. 1, the surfaceincluding inclined pairs of ultra-sonic emitters/detectors;

FIG. 4 is a schematic representation of a UAV reconnaissance systemincluding a schematic representation of the micro UAV of FIG. 1; and

FIG. 5 is a flow diagram of a process of mapping and controlling egressof the UAV of FIG. 1 from a building or obstacle-cluttered environment.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

As a way of compensating for drift in motor control and general drift inthe UAV arising from variation is air pressure and/or local currents orthermal effects, one might consider the use of collision bars or pushrods (collectively “bumpers”) that strategically extend outwardly fromthe body of a UAV. In this way, the bumpers contact an obstacle andtherefore mitigate the temporary loss of control. However, this approachis considered to be compromising and generally ineffectual given thatrange and usefulness of the UAV are dependent upon overall weight andunobtrusiveness. In this respect, the bumpers add to the overall weight(thus limiting the payload capabilities of the UAV) and increase theoverall size of the UAV, thereby increasing the size of the UAV andpotentially decreasing aerodynamics and the ability to control flight ofthe UAV. In fact, the use of bumpers, while logical, is fundamentally atodds with the functional requirement for a UAV since the bumpers serveno purpose in collecting information, supporting payload (such as avideo camera) or improving manoeuvrability and overall responsiveness ofthe drone.

Turning to a preferred solution to the problem, the inventors haverecognized that the formation of an ultra-sonic “bubble” or envelopearound the UAV provides significant technical control advantages withoutsignificantly increasing overall UAV weight or component costs. Thisbubble is assembled from partially overlapping three-dimensional spatiallobes generated and detected by relatively inclined pairs ofemitters/detectors positioned on each relevant surface. The system,which is preferably an active system, emits and ping and then looks todetect an echo. In offsetting the nominal major axis for each spatiallobe, a hysteresis effect and/or an absolute but relative signalstrength in reflected signal strengths/timing can be used to refine moreaccurately the location of an obstructing object or structure. Inessence, each pair of sensors contributes diverging but bioptic (orstereo or 3D) data reflection components that permit a processor tointerpret and then generate (or otherwise assess) 3-D spatial imaging ofthe physical environment in which the UAV is currentlyactive/positioned. The bubble may be formed using ultrasonic techniquesor lower frequency sonar techniques, as will be readily understood. Theterm “sonar” will be used as a generalized form to cover and refer toeach spatial lobe and the overall bubble produced by theemitters/detectors.

The bubble or envelope extends from at least each of the side surfaces(i.e. front, back, left and right) of the UAV and, preferably, also fromtop and bottom surfaces to provide an encapsulating sphere having theUAV centrally located therein. Each sonar bubble is assembled from anarrow beam or multiple narrow beans that undergo a degree ofbeamforming to produce a suitably shaped spatial sonar bubble; theselobes are essentially balloon shaped.

FIG. 1 and that show plan and side schematic representations of a microUAV 10 according to a preferred embodiment of the present invention. Ina preferred embodiment, the UAV 10 is configured in a quadrocopter orfour-rotor cross arrangement. Control of UAV motion is achieved byaltering the pitch and/or rotation rate of one or more rotor discs12-20, thereby changing its torque load and thrust/lift characteristics.Other configurations made be used, but counter-rotating pairs of frontrotors and rear rotors positioned diagonally outwardly from corners of afuselage 22 of the drone and fore and aft (and either side) of a centrepoint 24 of the UAV. Although not shown as an optimized aerodynamicdesign, the plan view of the micro UAV shows four individual drive shafthousings 30 configured in an X-orientation with respect to a fuselage22, with each drive shaft housing (containing a drive shaft andassociated servo controllers) coupled to a generallyhorizontally-orientated rotor.

To emphasise the relative position of the drive shafts and spatial sonarlobes and overall sonar bubble, the fuselage 32 is illustrated having aplan view that is octagonal in shape. The front (F) of the fuselage ismarked in the drawing. Of course, many other fuselage configurations arepossible, although aerodynamic consideration and the presence of stealthtechniques with reflecting planar surfaces will be design considerationunderstood and applied by the skilled addressee. The diagram does notextend the lobes about the rotors, but this is solely to avoid thediagram from becoming overly cluttered. In practice, the lobes willextend around and beyond the rotor end points, with the controllersensitized to exclude very near-field echo associated with the rotors.

To address the issues of drift and/or inertial and non-available GPSnavigation, relative positioning and relative hold abilities of the UAV,FIGS. 1 and 2 further show the use of sonar emitters and detectors40-68, with these placed on the principle outward surfaces (i.e. front,rear, left, right, upper and lower surfaces) of the fuselage to providesonar coverage with respect to each major axis of motion. Consequently,pairs of deflectors produce overlapping lobes for each major surfaceand, in totality, a generally spherical envelope that has, at itscentre, the UAV 10. In FIGS. 1 and 2, sonar lobes 80-94 extend outwardlyfrom side surface, whereas sonar lobes 96, 98 project upwardly and sonarlobes 100, 102 project downwardly relative to the fuselage 22. Together,sonar lobes 80-102 produce the encapsulating sonar bubble that generallycompletely encases the fuselage and rotors, but may also include someblind spots.

Each emitter is controlled to produce a “ping” that produces arelatively narrow beam-shaped 3D spatial sonar lobe extending outwardlyof the fuselage 22 by approximately 2.00 metres (m) to 5.00 m. The widthof each sonar lobe is in the approximate region of about 150 millimetres(mm) to about 400 mm. The shape of the sonar lobes is tailored so as notto infer/impinge with the rotor positions, but generally to produce aneffective protection envelope that is sufficiently large so as to detectobstruction at a point in time and space that is earlier enough topermit local evasive action to be computed and executed (based on sonarimaging of the environment). For example, the reach of each sonar lobeis sufficient to compensate for typical in-building flight speeds (of afew metres per second) and retarding actions applied to the rotorsthrough rotor control by an on-board local controller. Beamforming andlimited dispersion of each sonar lobe from its directional pulsetherefore effectively compensate for the omission of coverage at therotors. Of course, it envisaged that a one or more sonar detectors couldbe positioned at the end of each drive shaft housing 30 to providespecific imaging capabilities extending on a line outwardly of the eachrotor, with this merely a design option that requires appropriate signalprocessing to provide sonar image. To avoid false positives on echoestriggered by rotor operation and rotor position, a preferred embodimentof the sonar system of the various preferred embodiments operates with ahold-time that ignores any echo that are too close to the drone to beuseful, i.e. a retuned echo is less than a predetermined period of timefrom the initial ping. In the space domain, this means that if the tipsof the rotors, say, 150 mm from the emitters, any bounced echoesconsidered to be closer that 150 mm is ignored.

Turning to FIG. 3, a surface (such as an upper or side surface) of theUAV fuselage is shown to include inclined pairs 40, 42, 48, 50 of sonaremitters/detectors. In this respect, the sonar emitter/detector pairs40, 42, 48, 50 are represented by circles with arrows that show thegeneral relative directional coverage area provided for each lobe withrespect to an adjacent lobe. With some dispersion and overlap of thesonar lobes, a bioptic effect is produced from which an understanding ofrelative position and/or drift can be calculation. The assessment can bebased on a triangulation calculation that uses a round trip timing forthe ping-echo and/or measured signal strength/quality in the echo.Signal strength/quality can therefore be used to compensate forinterference, although the short range and generally line of sightoperation of the sonar means that multipath is seldom a problem. By wayof example, an object 200 (such as a pillar or door frame) in the fieldof detection of sonar lobes 96, 98 may be at distance D₁ from a firstemitter/detector 42 and distance D₂ from a second emitter/detector 48,where D₁>D₂. Consequently, the received signal strength from an echoreceived at the first emitter/detector 42 and the secondemitter/detector 48 would be at a level S₁ and S₂, respectively, whereS₁<S₂. The elapsed time between sending the ping and receiving the echofor the first emitter/detector 42 and the second emitter/detector 48would be time T₁ and time T₂, respectively, with T₁>T₂. In othersituations, an object may simply only appear within one sonar lobe, withthis being sufficient to identify a potential obstruction and itsgeneral location relative to the UAV 10. Given an assessment of theenvironment, remote control and/or drift can be compensated at local UAVlevel, i.e. on a near instantaneous basis the controller 302 of the UAVcan suppress or correct movement in any one or multiple planes based onthe sensed relative position of objects/obstructions within the sonarbubble. This control is available irrespective of whether there isline-of-sight to the UAV or whether the UAV has access to external GPSdata or any referenced map or plan that potentially defines apredetermined flight path.

In operation, simultaneous sonar pulses (“pings”) are sent from everyemitter on every axis on the UAV 10. Detectors on each surface (whichdetectors are typically be collocated with their emitters) wait for,i.e. detect, echo responses (often many per sensor) and use thisinformation to build up an environment around the UAV 10. This processis not dissimilar to basic ultrasonic range finding used in carbumper/fender systems. The sonar bubble therefore tracks relativeposition of objects over time during active flight.

From a resolution perspective, the preferred embodiment makes use ofhigh resolution timing circuits to calculate time between pingtransmission and echo reception/detection. Similarly, the filters in thecircuit are matched to support high resolution. It has been appreciatedthat one can operate the system to average the sonar results to get astable result (like car sensors do), but this removes accurate timingsand also introduces a phase lag. Indeed, as sonar bounces off objects itcan produce constructive and destructive interference and “beating”. Toget around this, the various sonar forms have been characterised thatthe filter designed accordingly. From a functional perspective, thefilter has a very small phase lag, operates to detect the direction ofobjects in the sonar path (e.g. through detected signal strength) andremoves noise and beating from the responses to give multiple stableechoes and therefore an indication of direction of each object headingtowards or away from the sensor set. In following this functionalregime, better than mm resolution can be obtained with respect to timingand, post-processing, mm resolution in movement and location isachieved.

Since a sonar ping on a fixed object at a fixed distance can varyingslightly due to interference and path, these false positive can suggestactual movements. Consequently, a preferred embodiment takes a number ofsamples for each echo to determine if there is relative and continuingmovement in a certain direction or whether the detected echo is justassociated with jittering. By making this determination, the systemremoves the jitter or noise and just reacts to actual movement on allechoes.

The circuits therefore provide millimetre resolution and accuracy fromevery sonar sensor. Preferably, the system further calibrates for airtemperature. As will be appreciated, air temperature changes the speedat which sound travels, with this change bringing about slightdifferences in sonar response. Measurement of temperature may thereforebe used in conjunction with a look-up table to adjust for temperatureand/or humidity changes. Other correction techniques, readilyappreciated by the skilled address, may be employed.

FIG. 4 is a schematic representation of a UAV reconnaissance system 300including a schematic representation of the micro UAV 10 of FIG. 1

The UAV 10 is based around a control system 302 that is processor basedand which control system processes sonar data and remotely generatedinstructions 304 to effect control of UAV hardware and UAVreconnaissance functionality. A transceiver 305 (but at least areceiver) allows for RF communication to a remote control centre 307.For example, downlink communication to the UAV can provide flightcontrol instructions, whereas an uplink 307 may support codedtransmission of telemetry data gathered from the UAV and detailingoperation and/or streamed video and/or audio files.

The controller 302 of the UAV is coupled to a motor controller 311responsible for servo control of ailerons and the like. The motorcontroller 311 is further coupled to rotors 306-310 for individualcontrol thereof.

AV data equipment 312 for controlling and generally overseeing thecapture of video and/or still image data (including images in thevisible and/or infrared wavelengths) from a suitable camera 313 and/oraudio from a microphone 314. The camera 313 therefore allows fornon-line-of-sight operation.

The control system is, ultimately, down to design and may make use ofmultiple processors that are task-optimised.

The UAV 10 further includes memory 316, coupled to the controller 302,containing firmware and software and, optionally, RAM storage foraccumulating data acquired by the UAV in a reconnaissance role. If datais captured and stored, then real-time streaming may be limited.

As will be understood, the UAV 10 also includes a power supply 340, suchas a lithium rechargeable battery, providing power to the transceiver305, controller 302 and other components. Measured telemetry data isprovided to the controller 305 from one or more gyroscopes 342, one ormore magnetometers 344 and multiple accelerometers 346 that cooperatewith the firmware to assess local inertia movement in the UAV's variousdegrees of movement and thereby support navigation and identifyposition/orientation. The operation and configuration of thesemeasurement devices are well known, as is how they interact with amicroprocessor-based control system to provide real-time flight control.The accelerometers are typically configured to be low noise units thatapply filtering and compensation algorithms to remove noise and

The controller 302 is coupled to the sonar emitters/detectors to controlpings and process recovered echos from multiple detectors. As previouslyexplained the sonar system is extensive and associated with the numerousplanes of movement of the UAV 10.

The UAV may further include a GPS system 350 that makes use of satelliteposition.

In terms of remote control, the remote control centre 307 will includesome form of human machine interface (HMI) 309 that includes a displayallowing visual presentation of video data observed by the camera and acontrol interface (such as a joystick, pedals and a keyboard) that allowremote flying (or driving in the case of a wheel or track-based drone)of the UAV 10.

Advantageously, if the UAV 10 of the preferred embodiment is within abuilding, the sonar bubble is used to plot relative and actual movementof the UAV and the relative positions of objects. The plot of movementis therefore entirely independent of external GPS-based data, with theplot providing the UAV with an ability for independent control fromlearnt ingress into the building. More particularly, given that thecontroller receives a sonar picture of the environment and alsogyroscopic, course heading information (from the magnetometer) andapplied movement from the accelerometers, the controller 302 isconfigured to assemble a map and actual path of the UAV through theenvironment, e.g. rooms and floors in a building, which map and path arestored in memory 316. Consequently, independently of any remote control(but typically upon receipt of a downlink instruction 304 or uponabsence of any direct control instruction for a predetermined period oftime), the UAV references the memory and executes a rapid and automatedegress from the building through the reversal of the recorded UAV'smovements. The reversal of precisely recorded movement, in fact, meansthat a map of the building is not actually required given that themovement is relative to the obstacles and layout of the building andthat the UAV's movement is strongly influenced by the sonar bubble. Thismeans that the UAV 10 can be recovered either the location of the remotecontrol centre 307 or to a point where RF contact with the remotecontrol centre 307 is re-established. Of course, the sonar bubble isagain used as a cross-check on egress to confirm that nothingfundamentally has changed in the plotted environment and to ensure thatthe UAV remains in free space (and therefore away from potentialobstructions against which it could collide and be damaged). Thisextends the UAV's ability to operate in a GPS-deprived environment.

Turning to the situation of hover where the UAV is ideally stationary,the sonar bubble also acts to offset drift within servos and motorcontrols. It has been identified that the sensors tend to drift withvariations in temperature and also at each start-up. Specifically, ifthe UAV is turned on and set to hover in a test environment containingfixed near field obstructions detectable within the various sonar lobes,any change in response in the sonar-detected environment along anymovement axis indicates the presence of drift in the sensor or controlcircuits. For example, if an object is detected by front-, side- andbottom-facing sonar detectors, the controller 303 resolves the positionof the object in 3-axis. With the controller configured to monitoractual movement to a high degree (and ideally mm accuracy), thecontroller can calculate drift in the inertial sensors of the UAV 10based exactly on what the drift is and even without sonar lock.Consequently, by compensating for this sonar-measured drift andattaining substantially stationary hover, the UAV's controller 302 canself-calibrate and lock the UAV's on-board sensors and servos toeliminate completely this drift. The sonar bubble therefore supportsattainment of in-flight stability and provides an effective multi-axisinertial navigation system. Indeed, there is no reason whyre-calibration cannot be applied during a flight, provided that the UAVis set to a hover mode in an environment where wind turbulence isminimal, e.g. within a building. Consequently, sensor lock is improvedand can be updated during use of the UAV and incursion forreconnaissance purposes.

Of course, throughout flight and ingress of the UAV, data from thecamera (and optionally the microphone) are relayed back to the remotecontrol 307 for review and UAV control purposes.

In terms of determining whether an object within the sonar bubble isactive, e.g. the movement of a cat, the sonar-bubble of the presentinvention is also able to assist in resolving movement provided that theUAV is in a hover mode. Specifically, with the compensated drift in theinertial systems of the system of the preferred embodiment being in theregion of a few millimetres per minute, so long as the movement of theobject from which an echo is being received is less than that thesensor-locked compensated drift, the controller is programmed tointerpret the object as being stationary and therefore to cancel thedrift. If the movement from the detected echo is more than the drift inthe inertial systems, the controller can reasonably conclude that theobject is in fact moving. Therefore, in assembling the environmental mapbased on sonar tracking of objects, any object that is tagged as mobilecan be disregarded to the extent that data relating to the object ispositively excluded from the UAV's inertial navigation system.

From the perspective of using GPS data, the drone can (at least at thepoint of release) be assumed to be accurately mapped by the GPS system.However, with time and movement, GPS signal attenuation or satelliteloss is a genuine concern. The sonar bubble and relativetracking/movement procedure described herein therefore permits anassessment on the reliability of the GPS. Specifically, by trackingrelative movement of the UAV using the sonar bubble, an absoluteposition of the UAV is known locally to the controller relative to anominal reference location (such as the point of power-up or point ofentry into a building). If received GPS data does not tally with a netcalculated position of the UAV derived from absolute relative movementof the UAV and relative to the reference location, then the GPS data iscorrupted and can be considered unreliable. At this point, the local UAVcontroller 302 can disregard the GPS data or otherwise re-set its ownknown position within its GPS system based on the integration of datafrom its gyros, accelerometers, compass (magnetometer) and the sonarbubble. Inertial navigation data and inertial guidance is thereforeimproved.

FIG. 5 is a flow diagram 500 of a process of mapping and controllingegress of a UAV from a building or obstacle-cluttered environment.

After initiation of the UAV, the UAV 10 typically enters into andestablishes a hover mode 502; this is a calibration. The internalcontroller 302 controls the sending of sonar pings and recovers echoesfrom the various emitters/detectors. The controller then resolves 504whether movement has been detected in any access. In the affirmative506, the movement is created to drift and the controller 302 appliesappropriate compensation 508 to establish sensor lock. If there is noidentified movement (as resolved by the controller 302), the UAV isconsidered to the stable and reconnaissance and building ingress canbegin 510 under downlink instructions communicated by the remote controlcentre 307 (and as input by a user through the HMI 309).

During flight, the controller regulates the sending 512 of multi-axissonar pings from sonar letters on each of the faces associated withindividual movement and to particular axis; these pings produce theoverlapping server lobes described in relation to FIGS. 1 to 3. Thevarious detectors recover 514 echoes from objects and these echoespermit the controller to resolve 516 a 3-D spatial environment (butexcludes objects considered to be mobile). The local is therefore ableto assemble and store 518 a record of relative movement of the UAV.

During flight, it may be desirable to establish a hover mode and toundertake recalibration process of the various on-board sensors; this isshown by the optional except back to operational block 502.

Assuming that the fight continues, the controller assesses 520 whetherthere has been a loss of the control signal to which the UAV isgenerally responsive. In the affirmative 522, the UAV 10 may initiate anautomatic retrace 524 of its stored route until such time as the controlsignal is required (as determined by the controller a decision block526). Once the control signal is re-acquired, the UAV 10 may continuepenetration and reporting (flow path through controller decision block528 and a return to process flow step 512), or the controller 302 canreceive an instruction to recover the UAV through a planned egress andexit strategy 530.

Returning to the potential loss of the control signal, if there is noloss of a control signal (path 532) then the controller may make adetermination 534 as to whether there is a loss or discrepancy in GPSdata. In the affirmative 536, the controller may ignore future GPSinformation or otherwise recalibrate the position of the UAB 10 based onrecorded and absolute relative movement of the UAV. Again, the systemcan return to its principal control loop in which the controllerregulates the sending of sonar pings to assemble a sonar envelope usedfor spatial mapping. Of course, if there is no loss of GPS data then thesystem will generally operates to continue penetration and reportinguntil such time as the system (and particularly the controller of theUAV) is told to cease operation and be recovered under controlledflights to the motor control centre 307.

It will be appreciated that the precise execution of the variousfunctional steps exemplified in the flow diagram of FIG. 5 may bechanged and re-ordered and are therefore merely illustrative of some ofthe more significant functional events undertaken by the preferredembodiments of the present invention.

It will be further understood that unless features in the particularpreferred embodiments are expressly identified as incompatible with oneanother or the surrounding context implies that they are mutuallyexclusive and not readily combinable in a complementary and/orsupportive sense, the totality of this disclosure contemplates andenvisions that specific features of those complementary embodiments canbe selectively combined to provide one or more comprehensive, butslightly different, technical solutions.

It will, of course, be appreciated that the above description has beengiven by way of example only and that modifications in details may bemade within the scope of the present invention. For example, while apreferred embodiment describes the UAV as an aero drone, the principleof building a sonar bubble, a sonar-based sensor calibrating system andan egress mapping process through determination of a working environment(such as doors and furniture and relative clearances) in 3D space can beapplied to other forms of remotely controlled vehicle, includingreconnaissance cars. The term “UAV” should therefore be understood torelate to any form of powered, remote-controlled drone and not limitedto aerial (micro or nano) vehicles.

It will be understood that reference to a controller is reference anysuitable processor function, including application specific chips and,potentially, even an on-board server. Consequently, reference to acontroller should be understood to include one or more processor chipsthat combine to support full control and reporting of the UAV and nototherwise limited to just a single device (although this is alsoenvisaged if sufficient addressing and processing power is availablewithin that single device).

What is claimed is:
 1. A UAV containing a drive system for propelling the UAV through a spatial environment: a controller for controlling the drive system and overseeing operation of the UAV; a multiplicity of sonar emitters associated with different axes of travel of the UAV, each sonar emitter producing a sonar lobe extending outwardly in a specified direction along each of said different axes of travel, the sonar lobes combining to encapsulate the UAV in a sonar bubble; and a multiplicity of sonar detectors, each axis of travel associated with a plurality of sonar detectors, wherein the sonar detectors are coupled to the controller to permit the controller, in response to echoes reflected off objects within the sonar bubble, to interpret and then generate a 3-D image of the spatial environment in which the UAV is stationary or moving and within which spatial environment the objects are stationary or moving; and wherein the controller is configured or arranged automatically to moderate the drive system in response to an assessed position of objects in the 3-D image relative to the UAV such that the controller independently controls movement of the UAV through the spatial environment along each axes of travel.
 2. The UAV recited in claim 1, wherein the sonar bubble is assembled from partially overlapping three-dimensional spatial sonar lobes generated by relatively inclined pairs of sonar emitters.
 3. The UAV recited in claim 2, wherein at least two sonar detectors are associated with each direction long each axis of travel, and wherein the controller is configured or arranged to resolve detected variations at least one of signal strength and round trip timing for pings to and echoes from objects in the sonar bubble to assess a relative position and nature of those objects with respect to the UAV.
 4. The UAV recited in claim 2, wherein the sonar emitters simultaneously emit sonar pulses from every sonar emitter associated with each axis of travel.
 5. The UAV recited in claim 1, further comprising: motion and position sensors configured to measure absolute movements of the UAV in 3-D space; and a memory for storing the absolute movement of the UAV in the spatial environment as resolved by the controller having regard to the measure of absolute movements and the 3-D image constructed from object data acquired from use of the sonar bubble.
 6. The UAV recited in claim 1, wherein object data acquired from use of the sonar bubble is used to compensate drift in at least one of the motion and position sensors.
 7. The UAV recited in claim 5, wherein object data acquired from use of the sonar bubble is used to compensate drift in at least one of the motion and position sensors.
 8. The UAV recited in claim 5, wherein object data determined as being within a predetermined minimum distance of the UAV is excluded from said generated 3-D image of the spatial environment.
 9. A method of controlling movement of a UAV through 3-D space, the method comprising: generating a sonar bubble that substantially encapsulates the UAV, the sonar bubble assembled from overlapping beamformed sonar lobes produced from sonar pings emanating from a multiplicity of sonar emitters on the UAV, the sonar emitters associated with directions of movement of the UAV through the 3-D space; in response to echoes reflected off objects within the sonar bubble following production of said beamformed sonar lobes and as detected by a multiplicity of sonar detectors on the UAV, having a controller in the UAV interpret and then generate a 3-D image of the spatial environment in which the UAV is stationary or moving and within which spatial environment the objects are classified as stationary or moving; and having the controller independently and automatically control movement of the UAV through the spatial environment by applying direct control to a drive system tasked with effecting movement in each axis of travel.
 10. The method of controlling movement of a UAV recited in claim 8, the method further comprising: measuring absolute movements of the UAV in 3-D space using motion and position sensors; storing in memory the absolute movement of the UAV in the spatial environment as resolved by the controller having regard to the measure of absolute movements and the 3-D image constructed from object data acquired from use of the sonar bubble; and under automatic instruction from the controller and with reference to the memory, automatically re-tracing the movement of the UAV upon loss of an external control signal or upon receipt of an instruction received over a wireless link.
 11. The method of controlling movement of a UAV recited in claim 8, further comprising: establishing a hover mode in the UAV; and based on distance measurement data to objects acquired from use of the sonar bubble, compensating for drift in at least one motion or position sensor in the UAV. 